A high density plasma (HDP) chemical vapor deposition (CVD) chamber is an apparatus for forming a film on a wafer. The wafer is supported by a carrier and has a surface exposed to the interior of the HDP CVD chamber. Conventional HDP CVD chambers have nozzles which spray gas into an electrically induced plasma region in the chamber interior. The plasma then reacts to form a film on the wafer. The nozzles of a conventional HDP CVD chamber are spaced about the chamber above a top surface of the wafer.
The film formed on the wafer using conventional techniques has significant variation in thickness across the surface of the wafer. Variations in thickness impacts the ability to form an intended semiconductor device using the wafer. For example, a relatively thicker portion of the film will take longer to etch, the result being either over-etching thinner portions of the film or under-etching thicker portions. Also relatively thinner portions of the film are removed faster during chemical and mechanical polishing (CMP), resulting in either damaging layers under the film if the thicker portions of the film are removed or a rougher surface if CMP stops once the thin portions of the film are removed.
Thickness profiles for films deposited on wafers are evaluated using mean thickness, standard deviation of the thickness across the wafer surface and thickness range. These values are determined by taking thickness measurements at various locations across the surface of the wafer. The more uniform the thickness profile, the more likely the wafer will produce a usable device.